C# 如何将 Expression<Func<T, bool>> 转换为 Predicate<T>
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How to convert an Expression<Func<T, bool>> to a Predicate<T>
提问by Lance Fisher
I have a method that accepts an Expression<Func<T, bool>>as a parameter. I would like to use it as a predicate in the List.Find() method, but I can't seem to convert it to a Predicate which List takes. Do you know a simple way to do this?
我有一个接受 anExpression<Func<T, bool>>作为参数的方法。我想将它用作 List.Find() 方法中的谓词，但我似乎无法将其转换为 List 采用的谓词。你知道一个简单的方法来做到这一点吗？
public IList<T> Find<T>(Expression<Func<T, bool>> expression) where T : class, new()
{
var list = GetList<T>();
var predicate = [what goes here to convert expression?];
return list.Find(predicate);
}
Update
更新
Combining answers from tvanfosson and 280Z28, I am now using this:
结合 tvanfosson 和 280Z28 的答案，我现在正在使用这个：
public IList<T> Find<T>(Expression<Func<T, bool>> expression) where T : class, new()
{
var list = GetList<T>();
return list.Where(expression.Compile()).ToList();
}
采纳答案by Sam Harwell
Func<T, bool> func = expression.Compile();
Predicate<T> pred = t => func(t);
Edit: per the comments we have a better answer for the second line:
编辑：根据评论，我们对第二行有更好的答案：
Predicate<T> pred = func.Invoke;
回答by tvanfosson
I'm not seeing the need for this method. Just use Where().
我不认为需要这种方法。只需使用 Where()。
var sublist = list.Where( expression.Compile() ).ToList();
Or even better, define the expression as a lambda inline.
或者更好的是，将表达式定义为 lambda 内联。
var sublist = list.Where( l => l.ID == id ).ToList();
回答by Jon Skeet
Another options which hasn't been mentioned:
另一个没有提到的选项：
Func<T, bool> func = expression.Compile();
Predicate<T> predicate = new Predicate<T>(func);
This generates the same IL as
这会生成与以下相同的 IL
Func<T, bool> func = expression.Compile();
Predicate<T> predicate = func.Invoke;
